1. Field of the Invention
This invention relates to improvements in an internal combustion engine of the split type operable on less than all of its cylinders when the engine load is below a given value.
2. Description of the Prior Art
It is known and desirable to increase the efficiency of a multicylinder internal combustion engine by reducing the number of cylinders on which the engine operates under predetermined engine operating conditions, particularly conditions of low engine load. Control systems have already been proposed which disable a number of cylinders in a multicylinder internal combustion engine by suppressing the supply of fuel to certain cylinders or by preventing the operation of the intake and exhaust valves of selected cylinders. Under given engine load conditions, the disablement of some of the cylinders of the engine increases the load on those remaining in operation and, as a result, the energy conversion efficiency is increased.
As compared to normal internal combustion engines operating on all of the cylinders over the full range of engine load conditions, stable combustion is more essential for split type internal combustion engines adapted to operate on less than all of the cylinders under low engine load conditions. It is common practice in the field of split type internal combustion engines to equalize the number of cylinders disabled under low engine load conditions to the number of cylinders remaining in operation over the full range of engine load conditions. For example, six-cylinder, split-type internal combustion engines have been designed to have three cylinders disabled under low engine load conditions.
It is desirable to design the cylinders held active over the full range of engine load conditions to ensure stable operation under low speed and light load conditions and the cylinders disabled under low load conditions to achieve sufficient output power under high speed and high load conditions.
The present invention provides an improved split type internal combustion engine which can ensure stable operation under low load conditions and achieve sufficient output power under high load conditions.